Flatfishes breathe symmetrically: an experimental reappraisal.
Experimental analysis of the pressure changes in the respiratory cavities of the American winter flounder Pseudopleuronectes americanus, together with electromyographic recordings of key respiratory muscles and cineradiographic observations of the distribution of radioopaque dye, have revealed unequivocally that the respiratory current and underlying mechanisms are symmetrical. The respiratory apparatus, as in other teleosts, is driven by bilaterally symmetrical alternating buccal pressure and opercular suction pumps. An elaborate deflecting apparatus is present in the respiratory cavities of flatfishes to maximize the irrigation of gills of both sides. Functional symmetry is maintained in the morphologically asymmetrical flatfishes and a high premium is put on the bilateral distribution and opercular ejection of the respiratory current during the evolutionary radiation of the Pleuronectiformes.